The present invention relates to an aluminum alloy brazing sheet for use, for example, in heat exchangers of automobiles.
For example, a conventional radiator of a heat exchanger for use in automobiles has a structure as shown in FIG. 1. The radiator is manufactured by the steps comprising disposing corrugated fins 2 among tubes 1, through which a refrigerant flows; assembling a core 4, by attaching header plates 3 at both ends of the tubes 1, and, after brazing the assembled body, attaching a resin tank 5 to the header plate 3. The refrigerant is cooled by flowing it through the tubes 1 of a radiator having the construction described above.
Side surfaces of the core 4 are reinforced with side plates (not shown).
A thin sheet, of thickness about 0.1 mm, made of an alloy manufactured by adding about 1.5 wt % of Zn in an alloy prescribed in JIS-3003, is used for the fin.
The JIS-3003 alloy is used as a core alloy of an aluminum alloy brazing sheet, of thickness 0.2 to 0.4 mm, and a filler alloy is clad on one surface of the core alloy and a JIS-7072 alloy is clad on the other surface of the core alloy, as a sacrificial anode material, to prevent corrosion pits from occurring. This brazing sheet is seam-welded to form a cylinder with the sacrificial anode material inside (at the refrigerant side), or it is rolled into a cylinder with the sacrificial anode material inside (at the refrigerant side), and the cylindrical brazing sheet is brazed to the tube.
An aluminum alloy brazing sheet, of thickness 1.0 to 2.0 mm, made of the same materials used in the tube, is also used for the header plate 3. While the heat exchanger is required to be lightweight in recent years, corrosion resistance of heat exchanger members should be more improved when the members are made of thin sheet materials to reduce the weight of the heat exchanger.
Usually, corrosion resistance of the tube can be attained by making the electric potential of the surface of the clad material less noble than the electric potential of the core alloy, by using the sacrificial anode material clad on the inside of the tube (the refrigerant side), and by making the electric potential of the fin material integrated by brazing at the outside (the atmosphere side) of the tube, less noble than the electric potential of the tube material.
However, by brazing, Cu added in the core alloy diffuses into the sacrificial anode material and filler alloy, and Zn added in the sacrificial anode material diffuses into the core alloy, in the conventional three-layered material. Particularly, when the thickness of the sheet is about 0.2 mm or less, Cu and Zn may diffuse across the total thickness of the sheet, by heating at about 600xc2x0 C., for the conventional brazing process, and thereby the potential difference in the direction of the thickness of the sheet is reduced, resulting in insufficient corrosion-resistance ability. When the amount of Zn to be added in the sacrificial anode material is greatly increased, to ensure a sufficient potential difference in the direction of the thickness of the sheet after heating for brazing, the electric potential at the sacrificial anode material side of the core alloy becomes less noble due to the diffusion of Zn. As a result, the electric potential (corrosion potential) distribution in the direction of the thickness of the sheet has a peak in which the electric potential at the outer side (the atmosphere side) is noble as compared with that at the center of the sheet in thickness (see FIG. 2).
Once corrosion pits are occurred at the inside of the tube (at the refrigerant side), they spread over the surface and advance in the direction of depth. However, portions less noble in electric potential prevent portions noble in electric potential from being corroded in the brazing sheet. Consequently, when the noblest portion having the highest electric potential (the peak position) within the brazing sheet, is located at the outside (at the atmosphere side) from the center of the thickness of the sheet, the electric potential gradient from the sacrificial anode material to the peak position is so reduced that the corrosion-resistance ability is insufficient. The distance to the peak position becomes small at the outside (at the atmosphere side) of the tube, to reduce the portions that serve as a sacrificial corrosion resistive layer. When the corrosion pits advance beyond the electric potential peak position in the direction of the thickness of the sheet, advance of corrosion is accelerated, to cause penetration holes, since the tip of the corrosion pit is less noble in electric potential than the surrounding portions of the pit.
The present invention is an aluminum alloy brazing sheet that has a four-layered structure, of sheet thickness 0.2 mm or less, and that comprises a core alloy, a filler alloy composed of an Alxe2x80x94Si alloy on one surface of the core alloy, a sacrificial anode material composed of an Alxe2x80x94Zn alloy on the other surface of the core alloy, and an intermediate layer between the core alloy and the sacrificial anode material, wherein the core alloy is composed of an Al alloy comprising 0.1 to 0.5 wt % of Si, 0.2 to 0.8 wt % of Fe, 0.5 to 2.0 wt % of Mn, and 0.05 to 0.5 wt % of Cu, with the balance being made of Al and unavoidable impurities, and wherein the intermediate layer is composed of an Al alloy comprising 0.1 to 0.5 wt % of Si, 0.2 to 0.8 wt % of Fe, 0.5 to 2.0 wt % of Mn, and 0.4 to 1 wt % of Cu, with the balance being made of Al and unavoidable impurities.
Further, the present invention is an aluminum alloy brazing sheet that has a four-layered structure, of sheet thickness 0.2 mm or less, and that comprises a core alloy, a filler alloy composed of an Alxe2x80x94Si alloy on one surface of the core alloy, a sacrificial anode material composed of an Alxe2x80x94Zn alloy on the other surface of the core alloy, and an intermediate layer between the core alloy and the sacrificial anode material, wherein the core alloy is composed of an Al alloy comprising 0.1 to 0.5 wt % of Si, 0.2 to 0.8 wt % of Fe, 0.5 to 2.0 wt % of Mn, and 0.05 to 0.5 wt % of Cu, with the balance being made of Al and unavoidable impurities, and wherein the intermediate layer is composed of an Al alloy comprising 0.1 to 0.5 wt % of Si, 0.2 to 0.8 wt % of Fe, 0.5 to 2.0 wt % of Mn, 0.4 to 1 wt % of Cu, and 0.2 to 1.5 wt % of Mg, with the balance being made of Al and unavoidable impurities.
Still further, the present invention is an aluminum alloy brazing sheet that has a four-layered structure, of sheet thickness 0.2 mm or less, and that comprises a core alloy, a filler alloy composed of an Alxe2x80x94Si alloy on one surface of the core alloy, a sacrificial anode material composed of an Alxe2x80x94Zn alloy on the other surface of the core alloy, and an intermediate layer between the core alloy and the sacrificial anode material, wherein the core alloy is composed of an Al alloy comprising 0.1 to 0.5 wt % of Si, 0.2 to 0.8 wt % of Fe, 0.5 to 2.0 wt % of Mn, 0.05 to 0.5 wt % of Cu, and 0.05 to 0.2 wt % of Mg, with the balance being made of Al and unavoidable impurities, and wherein the intermediate layer is composed of an Al alloy comprising 0.1 to 0.5 wt % of Si, 0.2 to 0.8 wt % of Fe, 0.5 to 2.0 wt % of Mn, 0.4 to 1 wt % of Cu, and 0.2 to 1.5 wt % of Mg, with the balance being made of Al and unavoidable impurities.
Other and further features, and advantages of the invention will appear more fully from the following description, take in connection with the accompanying drawings.